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effectiveness of lateral wedge in people with medial knee osteoarthritis

Discussion in 'Biomechanics, Sports and Foot orthoses' started by carol.yuen, Jun 15, 2016.

  1. carol.yuen

    carol.yuen Member

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    Hi all, I am keen to start my research project on the effectiveness of lateral wedge (full length or heel wedge) to improve the pain in people with stage 1 and stage 2 medial knee osteoarthritis.

    The mechanical factor of genu varum is associated with a four-fold increase in the odds of medial knee osteoarthritis over an eighteen months follow-up(Chang et al., 2004). Knee osteoarthritis with genu varum deformity is characterised by ground reaction force vector generated at plantar aspect of foot pass medially to knee joint centre. The knee adduction moment (KAM) arm is increased as the knee is in varus position leading to an increase in magnitude of external knee adduction moment (EKAM) (see Figure 1) (Hinman & Bennell, 2009). A greater EKAM increases loading of knee joint believed to be associated with pain (Sasaki & Yasuda, 1987). The calcaneus is assumed perfectly aligned with the tibia and that the subtalar joint (STJ) axis is directly in the centre of these two segments, the ground reaction force will exert a slight STJ supination moment(van Gheluwe, Kirby, & Hagman, 2005). The laterally wedging insole shifts the centre of pressure laterally to realign the mechanic axis of ankle, knee and hip joints.

    As we aware that there is a small number of people (approximate 15%) have perfectly aligned with tibia and STJ axis is directly in the center of these two segments.

    My question are the clinical results of those "normal" patients of using lateral wedging. What are FPI of those patients with medial knee osteoarthritis?

    Many thanks!
  2. efuller

    efuller MVP

    Some comments:
    It's good that you know to include the external when talking about knee adduction moment.

    I'm not sure why you included the comment about the assumption of the calcaneus being in line with the tibia and the comment about the STJ axs location. If you are looking at knee moment then you don't really care about STJ axis location of FPI. Do you have any data that says that those variables are related? What you do care about is center of pressure under the foot and center of pressure at the knee as this is what determines external knee adduction moment. I don't think you can externally measure center of pressure of the knee. I'm not sure about that. So, you have to make the assumption that the change in frontal plane knee moment comes from a change in the location of center of pressure under the foot.

    Are you aware of the maximum eversion height measurement. As you ask patients to evert their foot, some will have a higher range of eversion range of motion of the midfoot and STJ and some will have a lower range of motion. My sense is that the maximum eversion height does not correlate at all with FPI. An interesting part of your study would be to look at change in location of center of pressure with added wedge versus high or low maximum eversion height measurement. My thinking is that when you place the lateral wedge udner the feet with eversion range of motion, eversion will occur without necessarily changing the location of center of pressure. There may have been a study that sort of looked at this.

  3. carol.yuen

    carol.yuen Member

    thank you so much for your comments. they are very helpful.
    yes you are right. i assume how much of the distance of COP shift laterally is highly correlated to FPI. the distance of COP shifted is correlated to force of EKAM. FPI and STJ axis is highly correlated. FPI can tell me how much of ROM of rearfoot (eversion) with lateral wedges.

    I agreed FPI is not related to ROM of MTJ. My second thought is about mid tarsal joint plane of motion axis. I read studies from Dr Kirby and Dr Van Langelaan. Dr Van Langelaan found MTJ has multiple plane of motion. It can explain why the effectiveness of lateral wedge is varied to different pt. It may be caused by MTJ axis, particularly, full length lateral wedge is more effective than heel wedge. :) I need more data to prove my theory. ;-0

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